The present invention relates to an improved dual rechargeable battery arrangement having cells that are optimized for a high capacitance, and cells that are optimized for a high power output.
For the power scaling in the case of electrochemical energy storage systems in a vehicle, capacitance-optimized accumulator cells and power-optimized accumulator cells or dual-layer capacitors are installed in an accumulator arrangement in a mixed fashion, which is usually called a dual accumulator in the state of the art. As a rule, a string or several strings of capacitance-optimized cells are connected parallel to one string or several strings of power-optimized cells. As a rule, the strings are coupled by means of a DC-to-DC converter which is connected parallel to the strings. The DC-to-DC converter compensates different voltages between the strings.
German Patent Documents DE 20 2009 017 862 U1 and DE 20 2008 017 499 U1 describe parallel connections of batteries.
It is a disadvantage of the state of the art that the DC-to-DC converter has to be designed for the maximal peak power of the connected string. Such a DC-to-DC converter requires high expenditures and results in high costs.
It is an object of the invention to create an improved accumulator arrangement having cells that are optimized for a current output and having cells that are maximized with respect to capacitance.
The object of the invention is achieved by an accumulator arrangement having a first plurality of series-connected first charge storage cells, a second plurality of series-connected second charge storage cells and a third plurality of series-connected third charge storage cells. According to the invention, the accumulator arrangement has a first converter, to whose first connection pair the third plurality of series-connected third charge storage cells is connected. The second connection pair of first converters is connected in series with the first plurality of series-connected first charge storage cells. The series connection of the first plurality of first charge storage cells and the first converter is connected parallel to the second plurality of second charge storage cells. The first converter is designed for converting the voltage supplied by the third plurality of series-connected charge storage cells and/or the current supplied by the third plurality of series-connected charge storage cells and outputting it at the second connection pair. The lowest potential of the second plurality of series-connected second cells forms a first connection of the accumulator arrangement, and the highest potential of the second plurality of series-connected second cells forms a second connection of the accumulator arrangement.
The accumulator arrangement may be connected, for example, by way of a contactor, to an inverter, to which an electric machine can be connected.
According to the invention, the first converter, which can replace the DC-to-DC converter of the state of the art, is not connected parallel by way of an entire cell string but only by way of a part of a string of series-connected charge storage cells. The first converter therefore does not have to be designed for the maximal peak power, but only for the part of the peak power that can be drawn by means of the third charge storage cells of the accumulator arrangement.
The accumulator arrangement may further have a second converter, whose first connection pair is connected to an energy source, particularly the second plurality of second charge storage cells, and whose second connection pair is connected to the third plurality of third charge storage cells. The second converter is designed for transporting an electric charge from an energy source, particularly the second plurality of second charge storage cells, to the third plurality of charge storage cells. By means of the second converter, the third charge storage cells can be charged and/or discharged. The energy source may be an electric machine in the generator operation, an arbitrary charging device or an electrochemical energy storage system.
The accumulator arrangement may have a third converter and a fourth plurality of series-connected fourth charge storage cells, which is connected to the first connection pair of the third converter. The second connection pair of the third converter is connected in series with the second plurality of second charge storage cells. The third converter is designed for converting the voltage supplied by the fourth plurality of series-connected charge storage cells and/or converting the current supplied by the fourth plurality of series-connected fourth charge storage cells and outputting them at the second connection pair of the third converter. By means of the first converter, it can be adjusted whether more charge of the first plurality of series-connected first charge storage cells and of the third plurality of series-connected third charge storage cells or of the second plurality of series-connected second charge storage cells is drawn. By means of the third converter, it can be adjusted which voltage is generated by the series connection of the second plurality of series-connected second charge storage cells and fourth plurality of series-connected fourth charge storage cells. As a result, the intermediate circuit voltage can be adjustable, which is present between the first connection and the second connection of the accumulator arrangement. As a result of the obtained degree of freedom of the adjustable intermediate circuit voltage, the drive system can be operated in an efficiency-optimized manner and, in addition, the armature setting range of the electric machine can be expanded.
The accumulator arrangement may further have a control device which is designed such that, if a machine connected to the accumulator arrangement, for a predefined period of time, in a dynamic operating condition, has a higher current consumption than in a static operating condition, the control device activates the first converter such that charge is drawn from the first plurality of series-connected first charge storage cells and the third plurality of series-connected third charge storage cells. The control device may also be designed such that, if the electric machine, for a predefined time period, has a constant power consumption, the control device activates the first converter such that charge is drawn only from the second plurality of series-connected second charge storage cells. This operating condition will then be relevant if the second cells are designed such that they have a capacitance that is as high as possible, and the first and third cells are designed for a current output that is as high as possible. A dynamic operating condition may be an increased torque output for a predefined period of time, for example, for accelerating a vehicle.
In the dynamic operating condition, charge can be drawn from the first plurality of series-connected first charge storage cells, from the second plurality of series-connected second charge storage cells and from the third plurality of series-connected third charge storage cells.
The control device may be designed such that, if the electric machine, for a predefined period of time, in a dynamic operating condition, has a higher current consumption than in a static operating condition, the control device activates the first converter such that the sum of the output voltage of the first converter and of the plurality of first charge storage cells is higher than the idling voltage of the second plurality of series-connected second charge storage cells. If, for a predetermined time period, the electric machine has a constant power consumption, for example, in a static operating condition, the control device can activate the first converter such that the sum of the output voltage of the first converter and of the first plurality of first charge storage cells is lower than the idling voltage of the second plurality of second charge storage cells.
The control device may also be designed such that, if the electric machine, for a predefined time period, during a dynamic operating condition, has a higher current consumption, the control device activates the first converter such that charge of the second plurality of series-connected second charge storage cells is drawn. If a constant power consumption takes place for a predefined period of time, the first converter can be activated by the control device such that charge is drawn only from the first plurality of series-connected first charge storage cells and the third plurality of series-connected third charge storage cells. This operating condition is relevant if the second charge storage cells are designed for a current output that is as high as possible, and the first and third charge storage cells are designed for a capacitance that is as high as possible. It is understood that, during the dynamic operating condition, charge can be drawn from the first plurality of first charge storage cells, the second plurality of second charge storage cells and the third plurality of third charge storage cells.
The control device is further designed such that, if the electric machine has a higher current consumption for a predefined period of time during a dynamic operating condition, the control device activates the first converter such that the sum of the output voltage of the first converter and of the first plurality of series-connected first charge storage cells is higher than the idling voltage of the second plurality of series-connected second charge storage cells. If the electric machine has a constant power consumption for a predefined period of time during a static operating condition, the control device can activate the first converter such that the sum of the output voltage of the first converter and of the first plurality of first charge storage cells is lower than the idling voltage of the second plurality of second charge storage cells.
The control device may be designed such that, if an electric machine connected to the accumulator arrangement has a higher current consumption for a predefined period of time, the control device activates the third converter such that charge is drawn from the first plurality of series-connected first charge storage cells, and, if the electric machine has a constant power consumption for a predefined period of time, the control device activates the third converter such that charge is drawn from the second plurality of series-connected second charge storage cells and the fourth plurality of series-connected fourth charge storage cells. This operating condition may be relevant if the first and third charge storage cells are optimized for a current output that is as high as possible, and the second and the fourth charge storage cells are optimized for a capacitance that is as high as possible.
The control device may be designed for controlling the second converter such that electric charge is drawn from the second plurality of second charge storage cells and is supplied to the third plurality of third charge storage cells. The control device can thereby control the recharging of the third plurality of series-connected third charge storage cells.
The first charge storage cells and the third charge storage cells may be designed or optimized for a higher current output or shorter current output than the second charge storage cells and the fourth charge storage cells. The second charge storage cells and the fourth charge storage cells may be designed or optimized for a higher capacitance than the first charge storage cells and the third charge storage cells. The first charge storage cells and the third charge storage cells may have a capacitor, for example, a so-called Supercap, double layer capacitors or the like. The second charge storage cells and the fourth charge storage cells may have an accumulator, such as a lithium-ion accumulator or the like.
The number of third charge storage cells may amount to fewer than approximately 25%, preferably fewer than approximately 20%, most preferably fewer than approximately 10% of the number of first charge storage cells. As a result the first converter has to be designed to be less powerful, whereby it can be manufactured at lower expenditures and requires less installation space in the vehicle or the accumulator arrangement.
The invention also relates to a drive system for a vehicle having an electric drive with the above-described accumulator arrangement, an inverter and an electric machine, wherein the connections of the accumulator arrangement, which form the intermediate circuit voltage, are connected by way of a contactor to the direct-current connections of the inverter, and the electric machine is connected to the alternating current connections of the inverter. The electric machine may operate as a drive motor and/or as a generator.
The control device may be designed for activating the second converter in the generator operation such that it charges the charge storage cells designed for a higher current output, before it charges the charge storage cells designed for a higher capacitance. The control device may be designed such that it preferably charges the first plurality of series-connected first charge storage cells and the third plurality of series-connected third charge storage cells.
It is understood that the control device is designed such that it activates the first converter such that simultaneously energy is drawn from the first plurality of series-connected first charge storage cells, the third plurality of series-connected third charge storage cells and the second plurality of second charge storage cells, if the electric machine is to supply a torque, or energy is fed, if the electric machine is to operate as a generator. Particularly in the high-load case, electric charge is simultaneously withdrawn from the first plurality of series-connected first charge storage cells, the second plurality of series-connected second charge storage cells and the third plurality of series-connected third charge storage cells. In the partial-load case, the charge is drawn only from the second plurality of series-connected second charge storage cells.
It is preferred that the first charge storage cells and the third charge storage cells are designed or optimized for a higher current output. As a result, losses of the accumulator arrangement or of the drive system can be reduced that may possibly arise during the continuous operation by the first converter.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.